Electrochemically-aided control of solid phase micro-extraction (EASPME) using conducting polymer coated fiber.

摘要

Conducting polymers represent a class of new materials that have electronic conductivity. Polyacetylene was the first polymer that could be made conductive. The first experiments were conducted in the mid 1970s, and since then a number of other conducting polymers have been synthesized. The most important polymers are polyacetylene, polypyrrole, polythiophene, and polyaniline.; Conducting polymer films can be doped when exposed to an aqueous solution containing an analyte ion at a particular oxidizing potential. The dopant may be expelled when the polymer film is reduced to its neutral form by applying a constant reduction potential for a period of time.; Chemical speciation becomes important for trace metal analysis. It is not sufficient to quantitate the total elemental content of the samples to define toxicities. The principal analyzed compounds for the speciation of arsenic are arsenate, arsenite, dimethylarsenic acid (DMA), and arsenobetaine [(CH3)3As+CH2COO- ] and these have varying toxicities. Therefore, for the proper evaluation of the risks associated with the exposure of biological systems to arsenic compounds speciation must be investigated.; Solid Phase Micro-Extraction (SPME) using fused silica fibers coated with liquid polymeric materials such as poly(dimethylsiloxane) (PDMS) has been found to be a very useful technique for preconcentration of anions from environmental aqueous media. To maximize the uptake two criteria must be satisfied: the interaction energy of the fiber system must be large and the coating must be thick. On the other hand, they result in both unfavorable desorption thermodynamics and slow desorption kinetics. Therefore, SPME sampling and desorption in particular, can take as long as hours to perform.; Electronically conducting polymers such as poly (3-methylthiophene) (P3MT), and poly(3,4-ethylenedioxythiophene) (PEDOT) form cation radicals in the polymer matrix upon electro-oxidation. The material thus becomes hydrophilic and swells as it adsorbs water. In addition, to maintain electroneutrality in the matrix, anionic counter ions must be taken up from the solution phase. On switching the applied potential to negative values the polymer is reduced to its neutral (uncharged) state. The polymer matrix becomes hydrophobic and has a negative potential. The previously incorporated anions rapidly are expelled from the polymer as a result of these two forces.